J . Org. Chem. 1995,60, 5284-5290
5284
Preparation of Stable Primary Enamines: l-Aminobutadienesby Allyl Grignard Addition to Aryl Cyanides Followed by Controlled Hydrolysis Gerhard Erker,* Michael Riedel, Sandra Koch, Tim Jodicke, and Emst-Ulrich Wiirthwein*I+ Organisch-Chemisches Institut der Universitat Miinster, Corrensstrasse 40, 0-48249Miinster, Germany Received February 28, 1995"
From thermochemical data it is suggested that l-aminobutadienes are more stable than their nonconjugated imine tautomers by about 2 kcal mol-'. High level ab initio calculations have established the thermodynamic preference of the conjugated primary enamines over their P,yunsaturated ketimine isomers in the gas phase. This general prediction of an increased stability of primary enamines by butadiene conjugation has been confirmed experimentally with a variety of representative examples. Allyl Grignard addition to a number of aryl or hetaryl cyanides followed by controlled hydrolysis yields the respective 8,y-unsaturated ketimine systems that subsequently rearrange completely to their l-aminobutadiene isomers. Rearrangement to the thermodynamically more favored a,B-unsaturated imine tautomers is kinetically inhibited and, hence, not observed in these systems. In some cases conjugated enamine formation is already observed at the stage of the organometallic intermediates.
Introduction The primary enamine * imine tautomeric equilibrium is strongly dependent on substituents attached at carbon atoms in the a- and 8-positions to the functional group. Carbonyl substituents a t C1 destabilize the ketimine isomer 2 and thus lead to a high enamine concentration under equilibrium conditions. Carbonyl groups at C2, on the other hand, stabilize the carbanion character and thus strongly favor the enamine tautomer (2).l Experimental studies by H. Ahlbrecht2and others3have shown that alkyl and aryl groups at C 1 have only a negligible +
Quantum chemical calculations.
.-
influence on the enamine imine equilibrium whereas alkyl groups at C2 markedly disfavour the alkenamine. Aryl substituents at C2 increase the primary enamine stability; e.g. the tautomeric equilibrium 1 * 2 in chloroform is close to 1:l.
1
2
e Abstract published in Advance ACS Abstracts, July 1, 1995.
(1)Recent examples: Blake, A. J.; McNab, H.; Monahan, L. C. J. Chem. Soc., Perkin Trans 2 1991,2003.Barluenga, J.; del Pozo Losada, C.; Olano, B. Tetrahedron Lett. 1992,33,7579.Barluenga, J.; Tom&, M.; Ballesteros, A.; Santamaria, J.; Mpez-Ortiz, F. J. Chem. Soc., Chem. Commun. 1994,321.Erian, A. W.; Aziz, S. I.; Negun, A. M.; Sherif, S. M.; J. Chem. Res. (5') 1993,352.Koyama, H.; Kawato, T.; Kanatomi, H.; Matsushita, H.; Yonetani, K. J. Chem. Soc., Chem. Commun. 1994, 579. Reviews: Reinhoudt, D. N. Adv. Heterocycl. Chem. 1977,21, 253. Hickmott, P. W. Tetrahedron 1982,38,2050. Cook, A. G. Enamine Synthesis, Structure and Reactions; Marcel Dekker: New York, 1988.Chiang, Y.; Kresge, A. G. Science 1991,253, 395.Erian, A. W. Chem. Rev. 1993,93,1991.Patai, S.;Rappoport, Z. (Series Eds.). The Chemistry of Functional Groups: The Chemistry of Enamines, Z. Rappoport, Ed.; Wiley: New York, 1994. (2)Ahlbrecht, H.; Krohnke, F. Liebigs Ann. Chem. 1967,701, 126. Ahlbrecht, H. Tetrahedron Lett. 1968,4421. Ahlbrecht, H.; Rauchschwalbe, G. Tetrahedron Lett. 1971,4897.Ahlbrecht, H.; Papke, G. Tetrahedron Lett. 1972,4443.Tetrahedron 1974,2571. Ahlbrecht, H.; Hanisch, H.; Funk, W.; Kalas, R. D. Tetrahedron 1972,28, 5481. Ahlbrecht, H.; Fischer, S. Tetrahedron 1973,29,659.Ahlbrecht, H.; Blecher, J.; Hanisch, H.; Papke, G.; Reiner, M. T. Tetrahedron 1973, 29,3079.Ahlbrecht, H.;Funk, W.; Reiner, M. T. Tetrahedron 1976, 32,479. Ahlbrecht, H.; Kalas, R. D. Liebigs Ann. Chem. 1979, 102. See also: Duhamel, L.; Duhamel, P.; Legal, J.-C. Bull Soc. Chim. Fr. 1972,3230.Picard, J. P.; Aizpurua, J. M.; Elynsufi, A.; Kowalski, P. J. Organomet. Chem. 1990,391,13. (3)Pickard, P. L.;Vaughan, D. J. J.Am. Chem. SOC.1960,72,876. Pickard, P. L.;Polly, G. W. J. Am. Chem. Soc. 1964,76,5169.Clark, Shin, C.; Masaki, R. A.; Parker, D. C. J.Am. Chem. Soc. 1970,92,7257. M.; Onta, M. Bull. Chem. Soc. Jpn. 1971,44,1657.Ollinger, P.; Remp, W.; Junek, H. Monatsh. Chem. 1974,105,346.Pfau, M.; Ribiere, C. Bull SOC.Chim. Fr. 1971,2584.Brocas, J. M.; de Jeso, B.; Pommier, de Jeso, B.; Pommier, J.4. J.-C. J. Organomet. Chem. 1976,120,217. J. Chem. Soc., Chem. Commun. 1977,565.Ohtsuka, Y. J. Org. Chem. 1978,43,3231.Compagnon, P. L.;Gasquez, F.; Kimny, T. Synthesis 1966,948.Sevin, A.;Masure, D.; Giessner-Prettre, C.; Pfau, M. Helv. Chim. Acta 1990,73,552.Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J.Am. Chem. SOC.1992,114,1708.Smith, B. J.; Radom, L. J.Am. Chem. SOC.1992,114,36.Review: Shainyan, B. A.; Mirskova, A. N. Russ. Chem. Rev. 1979,48,107.
0022-3263/95/1960-5284$09.00/0
We have recently prepared l,Sdiamino-1,3,5-hexatrienes S4 by means of an organometallic template rea c t i ~ n .These ~ tail-to-tail-connectedconjugated primary enamines are very stable. A theoretical investigationhas revealed that such systems are thermodynamically stabilized primary enamines.6 It may be that the butadiene conjugation is sufficient to tip the enamine imine balance so far to the conjugated alkenamine side that the l-aminobutadiene tautomers become the only observed isomers under the conditions of thermodynamic control without the aid of further stabilizing functional group^.^^^ This idea is supported by our recent observa(4)Erker, G.; Pfaff, R.; Kriiger, C.; Nolte, M.; Goddard, R. Chem. Ber. 1992,125, 1669.Erker, G.; Pfaff, R. Organometallics 1993,12, 1921.Wingbermiihle, D.; Sarter, C.; Erker, G. Znorg. Chim. Acta 1994, 222,193.Erker, G.; Wingbermiihle, D.; Grehl, M.; Frohlich, R. Chem. Ber. 1994,127,1331. ( 5 )Erker, G.; Berlekamp, M.; Mpez, L.; Grehl, M.; Schonecker, B.; Krieg, R. Synthesis, 1994,212. For related template reactions see: Yasuda, H.; Tatsumi, IC;Nakamura, A. ACC.Chem. Res. 1986,18,120. Yasuda, H.; Nakamura, A. Angew. Chem. 1987,99,745. Angew. Chem., Int. Ed. Engl. 1987,26,723.Yasuda, H.; Okamoto, T.; Matsuoka, Y.; Nakamura, A,; Kai, J.; Kanehisa, N.; Kasai, N. Organometallics 1989, 8,1139. Erker, G.; Sosna, F.; Betz, P.; Werner, S.; Kriiger, C. J.Am. Chem. Soc. 1991,113,564.Erker, G.; Sosna, F.; Zwettler, R.; Kniger, C. Organometallics 1969,8,450.Erker, G.; Sosna, F.; Noe, R. Chem. Ber. 1990,123,821. Erker, G.; Sosna, F.; Zwettler, R.; Kriiger, C. 2. Anorg. Allg. Chem. 1990,581,16. Erker, G.; Sosna, F. Organometallics 1990,9,1949.Erker, G.; Sosna, F.; Pfaff, R.; Noe, R.; Sarter, C.; Krafi, A.; Kriiger, C.; Zwettler, R. J.Organomet. Chem. 1990,394,99.Erker, G.; Pfaff, R.; Kriiger, C.; Werner, S. Organometallics 1991, 10,3559. (6)Erker, G.; Pfaff, R.; Kowalski, D.; Wiirthwein, E.-U.; Krllger, C.; Goddard, R. J. Org. Chem. 1993,58,6771.
0 1995 American Chemical Society
J. Org. Chem., Vol. 60, No. 16,1995 6286
Preparation of Stable Primary Enamines tion that compounds containing a stable l-aminobutadiene subunit (7) have become available by a variation of our template synthe~is.~ This interpretation has been further supported by a theoretical investigation and by the development of a synthetic route to simple 1-aminobutadiene systems, both of which are described in this paper.
r-N
enaminehmine 10/11
(E)-8/(E)-12 (E)-8/9 (2)-8/(E)-12 (Z)-8/9 13/14 (E)-15/16 17/18
AE" 6-31+G*
AE"MP2/6-31+G*
6.14 6.24 0.42 7.02 1.19 6.63 2.89 6.78
5.77 5.15 -0.95 5.72 -0.38 5.92 1.35 4.87
a E n e r g y of t h e enamine relative to its best imine isomer, positive AE-values indicate that the enamine isomer is less favored under equilibrium conditions than t h e corresponding imine.
5
l3
Table 1. Calculated Energy Differences of Pairs of Enaminenmine Isomers (kcaVmol)
OH
If these values are applied to the 1-aminobutadiene(8) allylaldimine (9) equilibrium problem with the thermodynamic 1 * 2 1:l situation serving as the reference (see above), it is expected that the 8 9 equilibrium is shifted toward the enamine side by ca. 2 kcal mol-'. In other words, a conjugated enamine should be ca. 2 kcal mol-' more stable than its imine tautomer simply because of the l ,3-diene thermochemical conjugation energy, if the thermodynamic data of the corresponding
hydrocarbon systems are valid when nitrogen-containing substituents are attached at these frameworks. The validity of this assumption cannot be taken for granted, but it would be of a great general interest to know whether such thermochemical data, which have been measured with very high accuracy and are available for a great variety of hydrocarbon systems,1° can be reliably applied for such reactive substituted systems (as primary enamines or imines) from which such data are not easily available with sufficient accuracy experimentallybecause of their elusive nature or their high chemical reactivity. We have, therefore, studied the equilibrium between 1-aminobutadienes and their aldimine tautomers by quantum chemical calculations. Ab Initio Computational Studies. As in our previous study6 we again combine our experimental results with high level quantum mechanical ab initio calculations. The main question of this study concerns the relative energies of the various imindenamine tautomers in view of the thermodynamics and kinetics of possible mutual interconversions. The 6-31+G* basis setll of the GAUSSIAN 92 program package12was used throughout for complete geometry optimizations. All structures obtained correspond to minima on the potential energy surface as indicated by frequency calculations (NIMAG = 0). As previously, the differences in zero point energies of the enamines and the correspondingimines were found to be very small (Table 1);they are therefore not taken into explicit consideration in the determinations of the relative energies. Effects of electron correlations were estimated by use of second-order Mgller-Plesset the0137.l~ By calibration with a recent, very thorough theoretical study of the vinylamine-acetaldimine tautomerism by Lammertsma and Prasad,14we have recognized that our basis set employed produces a reasonable estimate for the equilibria in question. Both, the diffuse functions (+) and the inclusion of electron correlation (MP2) are essential for an adequate description of these systems. Thus, MP2/6-31+G*//6-31+G* total energies are the basis of the following discussion (total energies, zero point
(7)For related examples of conjugated tertiary enamines see: Potthoff, B.; Breitmeier, E. Chem. Ber. 1987, 120, 255. Snowden, R. L. S.; Brauchli, R.; Wiist, M. Helv. Chin. Acta 1990, 73, 640. Braisted, A. C.; Schultz, P. G. J.Am. Chem. Soc. 1990, 112, 7430. Katrizky, A. Lue, P. Tetrahedron Lett. 1991,32, 3597. Sustmann, R.; Long, Q.-H.; R.; Rogge, M.; Nuchter, U.;Bandmann, H. Chem. Ber. 1992,125,1647, 1657. Review: Hickmott, P. W. Tetrahedron 1984, 40, 2989. (8) For representative examples of syntheses of primary enamines under kinetic control see: Ripoll, J. L.; Lebrun, H.;Thuillier, A. Tetrahedron 1980,36,2497.Vallee, Y.; Ripoll, J.-L.; Maume, D. J.Anal. Appl. Pyrolysis 1988, 14, 171. (9) L6pez, L.; Berlekamp, M.; Kowalski, D.; Erker, G. Angew. Chem. 1994,106, 1168,Angew. Chem., Int. Ed. Engl. 1994,33, 1114. Breuckmann, R.; Lennartz, H.-W.; (10) Roth, W. R.; Adamczak, 0,; Boese, R. Chem. Ber. 1991, 124, 2499, and references cited therein.
(11) 6-31+G* basis set: Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. v. R. J. Comput. Chem. 1983,4, 294. (12) GAUSSIAN 92, Revision B, Frisch, M. J.;Trucks, G. W.; HeadGordon, M.; Gill, P. M. W.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley, J . S.; Gonzales, C.; Martin, R. L.; Fox, D. J.; DeFrees, D. J.; Baker, J.; Stewart, J. J . P.; Pople, J. A., Gaussian, Inc., Pittsburgh PA, 1992. (13)M ~ l l e rC.; , Plesset, M. S. Phys. Rev. 1934, 46,618. Frisch, M. J.; Krishnan, R., Pople, J. A. Chem. Phys. Lett. 1980, 75, 66. (14) Lammertsma, K.; Prasad, B. V. J.Am. Chem. SOC.1994,116, 642. See also: Pappalardo, R. R.; Marcos, E. S.; Ruiz-Lopez, M. F.; Rinaldi, D.; Rivail, J.-L. J.Am. Chem. SOC.1993,115,3722. Bouchoux, G.; Penand-Berruyer, F.; Nguyen, M. T. J . Am. Chem. SOC.1993,115, 9728.
'1) RCN
2) R;c=o
RsJo-
\Ln H
Ad
R'bJnEttb-nmR 7
6
NHZ
R = Aryl, Alkyl; R' = Aryl, Alkyl
Results and Discussion Theoretical Studies. The heat of hydrogenation of 1-butene is 30.2 kcal mol-'. The butadiene hydrogenation to butane is exothermic by 56.5 kcal mol-l under standard conditions, which is 3.9 kcal mol-' less than expected from the 1-butene reference value. This difference is attributed to the thermochemical conjugation energy of butadiene, i.e. the combined a- and nenergy that is gained by bringing two vinyl groups into conjugation.1° This effect is additive. The 1,3,5-hexatrieneheat of hydrogenation is 79.4 kcal mol-' which is 8.4 kcal mol-l less than the sum of the 1-butene(2x ) and trans-2-butene heats of hydrogenation. Thus the thermochemical conjugation energy of each CHz=CHCH=CH unit in 1,3,5hexatriene is 4.2 kcal mol-'. In contrast, the heat of hydrogenation of styrene (to ethylbenzene) is only 28.1 kcal mol-l; that means that the thermochemical conjugation energy of the arylalkene (2.1 kcal mol-l) is ca. 2 kcal mol-' less than that of butadiene.1°
-
-
6286 J. Org. Chem., Vol.60,No.16, 1995
Erker et al.
P?-K
2+w
Effeeds of additional n-conjugation by vinyl and phenyl substituents in a or B position of the parent vinylamine system were elaborated by computations of all of the possible conformers and configurational isomers of 1-and 2-aminobutadiene8,13 (for earlier MIND03 calculations see ref 15) and 1-and 2-aminostyrene 16,17 and of their respective imine isomers 9, 12, 14, 16, and 18. For the sake of clarity, only the energetically best structure of each system (global minimum) is discussed (see Figure 1 and Table 2).16 1-Aminobutadiene8 (CH2=CHCH=CHNH2). Our calculations predict the all-trans form (E)-8((E)-s-transconformation) to be lowest in energy of all possible conformational and configurational isomers (Erel= 0.00 kcal/mol); for instance, the (2)-s-trans-form (21-8 is by ca. 0.6 kcal/mol higher in energy. Among the possible imine forms, two tautomers have to be considered, the nonconjugated imine (l-azapenta-l,6diene) 9 and the conjugated l-azapenta-1,3-diene 12. As anticipated, the conjugated all-trans isomer (E)-12 corresponds to the global minimum of this part of the potential energy hyperface. This structure (E)-12 is favored by ca. 5.2 kcal/mol over the best 1-aminobutadiene form (E)-8;the corresponding isomer (21-12 with a ZC=N double bond is slightly (ca. 1.2 kcal/mol) less favorable. The effects of butadiene-liken-n conjugation in such systems amount to ca. 6 kcal/mol, as indicated by the relative energy of the nonconjugated 1-azapenta-1,Cdiene 9 (Erel = 6.09 kcdmol, compared to (E)-12). It is remarkable, that theory predicts a higher relative energy (ca. 1kcal/mol) for this isomer (9)than for the primary 1-aminobutadiene (E)-8. With regard to our experiments (vide supra) we conclude that the equilibrium of tautomers of l-aminobutadienes/l-azapenta-1,4-dienes by a formal 1,3 hydrogen shift lies on the side of the observed l-aminobutadienes for thermodynamic reasons. In contrast, our data indicate further that tautomerism of the l-aminobutadienes toward the thermodynamically more stable l-azapenta-1,3-dienes (like 12) by a formal 1,5 hydrogen shiff must be precluded for kinetic reasons, since obviously high activation barriers prevent the spontaneous isomerization. Experimental studies have often revealed slow tautomerization not only for enaminehmine equilibria, but also for enolization~." Thus, the unexpected stability of primary l-aminobutadienes is explained from our theoretical data from thermodynamic as well as kinetic argumentations. 2-Aminobutadiene 13 (CHZ=CHCH(NH~)=CHZ). Here, the thermodynamic situation of the enaminehmine tautomerism is quite similar. In fact, we again obtain the s-trans form 13as the best structure for the enamine tautomer. However, as before, the energy lowest (conjugated) imine tautomer (E)-14, featuring a 2-methyl-lazabutadiene structure, is favored by ca. 5.9 kcaYmo1, a value that is close to the 1-aminobutadiene data. This similarity is mainly due to the fact that the imine tautomer 14 and the 2-aminobutadiene 13 are both
+?$e E-12
QN oc OH Figure 1. Calculated minimum structures of isomeric enaminehmine pairs.
energies, a d dipole moments: Table 1;relative energies of the enamines, compared to their best imino tautomers: Table 2). Vinylamine 10 (H~C=CHNH~).Starting point for our discussion is the equilibrium of the parent vinylamine lO/acetaldimine 11system. Our computational method produces a thermodynamic difference of ca. 5.8 kcdmol in favor for the imine tautomer 11; the best literature value available (G2 theory) is 3.9 kcaVm01.l~Thus, we may expect, that our basis sets artificially overestimate slightly the stability of the imine tautomer. Inspite of the thermodynamics, which favor strongly the imine tautomer, according to literature data, vinylamines have a surprisingly long lifetime and are only slowly converted Thus, high actiinto the corresponding imine vation barriers are responsible for the relative kinetic stability of such primary enamines.
Table 2. Ab Initio Total Energies (au), Zero Point Energies (ZPE, kcallmol), and Calculated Dipole Moments (DM, Debye) of the Enaminenmine Isomers enamine 6-31+G* ZPE DM MP2/6-31+G* imine 6-31+G* ZPE DM MP2/6-31+G* 10 -133.06884(0) 46.45 1.554 -133.48990 11 -132.07862(0) 46.26 2.403 -133.49910 69-8
(21-8 13 (E)-lS 17
-209.95827(0) -209.95704(0) -209.95741(0) -362.62692(0) -362.62798(0)
69.11 69.28 69.26 101.43 101.48
2.089 1.874 1.232 1.883 1.257
-210.63201
(EM
-210.63110 -210.63169 -363.81075 -363.81358
(E)-12 (21-12 13 (E)-16 18
-209.95894(0) -209.96822(0) -209.96651(0) -209.96797(0) -362.63152(0) -362.63878(0)
69.19 69.06 69.07 69.14 101.52 101.53
2.167 2.820 3.632 2.727 2.179 2.318
-210.63050 -210.64021 -210.63833 -210.64113 -363.81290 -363.82134
Preparation of Stable Primary Enamines stabilized by significant n-conjugative interactions between C2 and C3 of the butadiene subunits. Since in this case no nonconjugated imine tautomer is possible, the observation of stable primary 2-aminobutadienes is predicted to be possible only for systems with high kinetic barriers between the two tautomers, but not for thermodynamic reasons. 2-Aminobutadienes have recently found interesting applications in acyclic and heterocyclic chemistry. 2-Aminostyrene 15 (PhCH=CHNH& For steric reasons, the (E)-isomer of 15 corresponds to the energy lowest enamine form. The phenyl ring is found to lie well in plane with the vinyl moiety. The best corresponding imine tautomer 16 is predicted to be lower in energy by ca. 1.4 kcaymol. Thus, we conclude, that in contrast to a vinyl group in the systems 8 , 9 , 1 2 a phenyl substituent in 2-position is not suited to overcome the thermodynamic preference for the imine form of the vinylamine/acetaldimine system 1 0 , l l . These theoretical results agree well with experimental observations by Ahlbrecht et al.;2they found varying mixtures of both compounds depending on temperature and solvent polarity. l-Aminostyrene 17 (CH2=C(NHz)(Ph)). Here, the thermodynamic situation of the enaminehmine equilibrium resembles much that of 2-aminobutadiene 13. The imine form 18 is strongly favored over the crossconjugated l-aminostyrene 17 (Erelof the enamine: 4.9 kcaymol), certainly due to the n-conjugation realized in the acetophenonimine tautomer 18; thermodynamic reasons disfavor the experimental observation of 17 in equilibrium with 18, but here as above, high activation barriers may well preclude the rapid equilibration. ExperimentalInvestigations. Our theoretical studies have suggested that l-amino-1,3-butadienes should be thermodynamically preferred over their nonconjugated imine tautomers. If they are kinetically protected from rearrangement to their conjugated imine tautomers,17 such conjugated primary enamines should be stable and easy to prepare by a variety of straightforward preparative routes, provided that hydrolysis to the related nitrogen free carbonyl systems is prevented. We have therefore reacted allylmagnesium chloride with a number of organic nitriles. The resulting magnesium containing addition products were then subjected to a controlled hydrolysis.l9 Several representative examples are described below. Allylmagnesium chloride, dissolved in diethyl ether, was slowly added to a solution of 2-cyanopyridineat room temperature. The organometallic addition product (see below) was isolated as a solid that was subjected to hydrolysis under various reaction conditions. Treatment with a small amount of water in a two-phase aqueous/ (15) Koikov, L. N.; Terent'ev, P. B.; Gloriozov, I. P.; Bundel', Yu. G. J. Org. Chem. U S S R (Engl. Transl.) 1984,20,832-838. (16)Details of the calculations corresponding to local minima are
available from E.-U. W. upon request. (17)For enols: Cederstav, A. K.; Novak, B. M. J. Am. Chem. SOC. 1994,116,4073.Bergens, S. H.; Bosnich, B. J . Am. Chem. SOC.1991, 113, 958.Capon, B.; Guo, B.-Z.; Kwok, F. C.; Siddhanta, A. K.; Zucco, C. Acc. Chem. Res. 1988,21,135.Keeffe, J. R.Kresge, A. J. in Patai, S.; Rappoport, 2. (Series Eds.). The Chemistry of Functional Groups: The Chemistry of Enols, Rappoport, Z., Ed.; Wiley, New York, 1990; Chapter 7,pp 399-480. For enamines: Capon, B.; Wu, Z.-P. J . Org. Chem. 1990,55,2317.See also references 1-3. (18)Barluenga, J.;Aznar, F.; Cabal, M.-P.; ValdBs, C. J . Chem. SOC. Perkin Trans. 1 1990,633.Lijpez-Ortiz, F.; Pelaez-Arango, E.; Palacios, F.; Barluenga, J.; Garcia-Granda, S.; Tejerina, B.; Garcia-Fernandes, A. J . Org. Chem. 1994,59,1984 and references therein.
J. Org. Chem., Vol. 60,No.16, 1995 5287
ethereal suspension resulted in mixtures of the enamine 22a and the corresponding ketone l-oxo-l-(2-pyridyl)but3-ene. Treatment of the magnesium compound with methanol led to a high amount of l-amino-l-(2-pyridyl)1,3-butadiene22a, but the product still contained a small quantity of carbonyl contaminations that could not be removed. Similarly, the reaction of the magnesium salt with HC1 in ether gave the enamine only contaminated. Attempted protonolysis with tert-butyl alcohol was unsuccessful in our hands to produce the enamine a t all. The best method for subsequent controlled hydrolysis of the allyl Grignardnitrile addition product was treatment of an ethereal suspension with a few drops of concentrated aqueous ammonia. Conventional workup of the ethereal phase after several minutes of stirring consistently and reproducibly gave the conjugated enamine product in reasonable yield and purity. From the reaction of 2-cyanopyridine with the allylmagnesium chloride reagent and subsequent controlled hydrolysis with aqueous ammonia in a two-phase system, as described above, we have isolated a single isomer of the enamine product, namely (lZ)-l-amin0-1-(2-pyridyl)l,&butadiene [(2)-22aIin 78%yield. The enamine shows IR (NH2) bands at Y 3467 and 3355 cm-l. It has a characteristic W absorption at Am= = 285 nm ( E 8900). The stereochemical assignment comes from a comparison with the lH NMR data of the related 1,6-diamino-l,6diaryl-1,3,5-hexatrienesystems 5, the stereochemistry of which was secured by two X-ray crystal structure analy(Z)-22ashows lH NMR signals (in benzenes e ~ Product .~ &) of the olefinic part of the molecule at 6 5.84 (2-H), -6.5 (3-H), 5.23 (4-Htrans), 5.00 (4-Hcis)with coupling 4-Htrans),3J = 11.1HZ (2constants 'J = 2.0 HZ (4-HCls, H, 3-H), 16.6 HZ (3-H, 4-Htrans), 10.2 HZ (3-H, 4-Hcis), 4J = 0.8 HZ (2-H, 4-Hcis)and 0.8 HZ (2-H, 4-Htrans). Our assignment is further supported by an irradiation experiment of the dienamine (Z)-22ausing 350 nm light that resulted in the formation of the (E)-22a isomer. Prolonged irradiation at 350 nm in benzene4 led to a photostationary equilibrium of (Z)-22a/(E)-22aof 52:48. The formation of (1Z)-l-amino-l-(2-pyridyl)-1,3-butadiene (Z)-22ais thermodynamicallycontrolled. We have hydrolyzed the organometallic allyl Grignard to (2cyanolpyridine addition product at -30 "C (aqueousN H 3 ) and immediately analyzed the obtained product mixture by lH NMR spectroscopy (in toluene-&). At 240 K the solution contains a 4:l imine to enamine mixture. We have detected two isomers of the nonconjugated imine 21 with a syn-2la:anti-2la ratio of 4:L2O The major product (syn-2la)is characterized by a lH NMR =NH resonance at 6 9.98 whereas the minor imine isomer exhibits its =NH signal at 6 11.90. The sample was slowly warmed to ambient temperature inside the NMR spectrometer and lH NMR spectra were monitored at several intermediate temperatures. During 7 h ca. 90% (19)Normal hydrolysis using aqueous acid, of course, leads to the formation of the corresponding ketones: Kharasch, M. S.; Reinmuth, 0. Grignard Reactions ofNonmetallic Substances, Prentice-Hall: New York, 1954; pp 769-772. Canonne, P.; Foscolos, G. B.; Lemay, G. Tetrahedron Lett. 1980,21,155. For related reactions see: Orita, A.; Fukudome, M.; Ohe, K.; Murai, S. J . Org. Chem. 1994,59,477.Dutt, M.; Fravel, B.; Ford, G. P.; Biehl, E. R. J. Org. Chem. 1994,59,497. (20)Ahlbrecht, H.; Fischer, S. Tetrahedron 1970,26, 2837.Staab, H. A,; Vogtle, F.; Mannschreck, A. Tetrahedron Lett. 1966, 697. Wurmb-Gerlich, D.; Vogtle, F.; Mannschreck, A.; Staab, H. A. Liebigs Ann. Chem. 1967,708,36.Karabatsos, G. J.;Lande, S. S. Tetrahedron 1968,24,3907. Hine, J.;Yeh, C. Y.; J . Am. Chem. SOC.1967,89,2669. Perry, K. A.;Robinson, P. J.; Sainsbury, P. J.;Waller, M. J. J. Chem. SOC.B . 1970, 700. Fraser, R. R.;Banville, J . Chem. SOC.,Chem. Commun. 1979,47.
Erker et al.
6288 J. Org. Chem., Vol. 60,No.16,1995 r
Scheme 1
'6NA
H N (M g CI 1
N[Mg C l l
Ce.. *-N
20a
190
o nti -2 1a
syndla ,
q+
hv
/
H eN\ H Z -220
1
/
=
5037
8''
N2' H
N2
H
E-22a
of the imines had tautomerized to the conjugated enamine (2)-22a under these conditions. ARer 32 h at ambient temperature only the primary enamine (2)-22a was present in the toluene-& solution. The question remains whether this imine conjugated enamine tautomerism can only be observed at the stage of the final metal free products or if the magnesiumcontaining addition products exhibit the same behavior. To answer this question we have dissolved the allylmagnesium chloridd2-cyanopyridineaddition product in tetrahydrofuran-& and detected the N-metalated ketimine system 19a by 'H NMR spectroscopy. The nonconjugated 1-iminobut-3-enemoiety shows very characteristic sig4.99 nals at 6 6.22 (m, lH, 3-H), 5.27 (m, lH, 4-Htrana), (m, lH, 4-H,is) and 3.94 (br d, 2H, CHd. During 12 h at room temperature the Mg-imine system 19a tautomerized completely. After that time under these conditions we have only detected the N-metalated conjugated enamine system 20a by 'H NMR spectroscopy in tetrahydrofuran-& solution ['H NMR signals at 6 6.82 (m, lH, 3-H), 5.52 (d, lH, 3J = 11Hz, 2-H), 4.73 (m, lH, 4-Htrans),4.40 (m, lH, 4-Hd,), 3.94 (br s, lH, NH)l. The reaction of 2-cyanofuran with allylmagnesium chloride proceeds similarly. lH NMR spectroscopy of the isolated organometallic adduct revealed that the primary product has a metalated ketimine structure ('H NMR in benzene-ddtetrahydrofuran-& (1O:l): 6 5.25 (m, lH, 4-Htrans)s 4.99 (m, lH, 4-&1s), 3.51 (d, 2H, 3J = 7.1 Hz, CH2)). With time, tautomerization to the enamine isomer is observed. During 12 h the initial 80:20 imine to enamine mixture has changed to a ca. 50:50 mixture of isomers. Hydrolysis of the organomagnesium addition product with aqueous ammonia furnished a single conjugated primary enamine product to which we have assigned the structure of (Z)-22b. In these systems the formation of the conjugated primary enamine from the /3, y-unsaturated ketimine is thermodynamically controlled. Therefore, it is surprising that in each of the above described systems only a single isomer of the 2-furyl- and 2-pyridyl-substituted enamine systems was obtained in the thermally controlled reactions. This may be due to some influence of the hetarene substituent because this clear preference of the Zalkenamine formation is lost when the heteroatom-free aryl substituents are employed.
-
Benzonitrile was treated with 1mol equiv of the allyl Grignard reagent and subsequently hydrolyzed under controlled conditions to give the conjugated primary 22c in 64% enamine l-amino-l-phenyl-l,3-butadiene yield. The product consists of a 70:30 mixture of the (2)2% and (E1-22~isomers (for details of their charaderization see the Experimental Section). Similarly, a 80:20 and (E)-22d was obtained from allylmagmixture of (2)nesium chloride and p-methylbenzonitrile while the reaction starting from 1-cyanonaphthalene gave (2)-22e and (E)-22e in a 85:15 ratio. Both cyano groups of terephthalic dinitrile were employed in the allyl Grignard additiodcontrolled hydrolysis sequence. We have isolated the correspondingp-phenylene bisenamine 22f in 65%yield as a mixture of three stereoisomers (80%major isomer).
1. e M 9 C I CN
2 -220
E-220
CN NH2
22f (3 stereoisomers)
As expected, our two-step reaction sequence can be used to prepare stable extended conjugated primary enamine systems as well. We have reacted transcinnamic nitrile with allylmagnesium chloride. Subsequent hydrolysis ( H z O M 3 )gave 3-amino-l-phenyl-1,3,5hexatriene in an overall yield of 72%. Again a mixture of two stereoisomers (LE,32)-22g and (LE,3E)-22g was obtained (70:30 ratio).
J. Org. Chem., Vol. 60, No. 16, 1995 5289
Preparation of Stable Primary Enamines
benzene-&). From the photostationary mixture the 'H NMR data of E-22a were obtained. 'H NMR (benzene-&): 6 8.40 Both the theoretical and the experimental work carried (m, lH), 5.58 (d, 1H, 3 J= ~ 11.3~ Hz), 5.09 (ddd, 1H, 3 J= ~ ~ 16.6 Hz, 'JHH = 2.2 Hz, *JHH = 1.3 Hz), 4.85 (ddd, 1H, 3 J= ~ ~ out in this study show that simple nonfunctionalized 10.1 Hz, 2 J= ~ 2.2 ~ Hz, 4 J= ~ 0.9 ~ Hz), 3.80 (S, 2H), four primary enamines are not as elusive as common feeling resonances of the pyridyl substituent under signals of (Z)-22a. of organic chemists may suggest. Conjugation of the NMR (benzene-&, DEFT): 6 155.0 (C), 149.4 (CH), 134.5 alkenamine moiety with a single carbon-carbon double (C), 135.6, 124.6, 122.7 (CH), 110.3 (CH), 105.6 (CH2). bond is sufficient to make the enamine tautomer therSpectroscopic Characterization of the Organometalmodynamically more favorable than its nonconjugated lic Products (19a, 20a) Obtained from the Allyl MagneB,y-unsaturated ketimines tautomer. On the other hand, sium Chloride Addition to 2-Cyanopyridine. The organothe a,B-unsaturated ketimines are by 5-6 kcal mol-l metallic addition product was collected by filtration as described above. A sample was dissolved in tetrahydrofuran-dg more stable than the corresponding 1-aminobutadiene and an 1H NMR spectrum of the metalated ketimine 19a, systems but there is convincing experimental evidence which was the major product ('80%) present in the solution, that the butadieneamine 4 1-azabutadiene equilibration was monitored. 'H NMR of l9a in tetrahydrofuran-dg: 6 9.18 has a high activation barrier under the conditions of our (d, lH, 3 J= 4.5 ~ Hz), ~ 8.10-7.75, 7.36 (each m, 3H), 6.22 (m, experimental investigation. Therefore, a great variety lH), 5.27 (m, lH), 4.99 (m, lH), 3.94 (d, 2H, 3 J= ~ 6.6 Hz). ~ of substituted 1-aminobutadienes can very easily be After 12 h at room temperature tautomerization to the prepared and studied. They are theoretically interesting metalated enamine 20a was almost complete. 'H NMR (tetrahydrofuran-&): 6 8.87 (m, lH), 7.82,7.62,7.11 (each m, 3H), molecules which are protected from rearrangement to 6.82 (m, lH), 5.52 (d, l H , 'JHH = 11Hz), 4.73 (br d, lH), 4.40 their nonconjugated alkenimine tautomers thermody(br d, lH), 3.94 (br s, 1H). namically and are prevented from isomerization to the l-Amino-l-(2-furyl)-1,3-butadiene (22b). Reaction of more stable conjugated alkenimines on kinetic grounds. 0.50 g (6.48 mmol) of 2-cyanofuran in 50 mL of ether with 13.5 The metastable conjugated primary enamine systems are mL of a 0.48 M ethereal allylmagnesium chloride solution gave easily prepared and isolated by the routes outlined above; 0.61 g (70%)of (Z)-22bas a slightly yellow colored oil. 'H N M R they represent potentially useful reagents in organic (benzene-&): 6 6.95 (m, lH), 6.36 (m, lH), 6.10, 6.02 (each synthesis, which deserve intensive further investigation. m, each lH), 5.85 (d, lH, 3 J= 11.4 ~ ~ Hz), 5.11 (ddd, 1H, 3 J ~ ~ = 16.6 Hz, 2 J= 2.1 ~ Hz, ~ JHH = 0.8 Hz), 4.92 (ddd, l H , 3 J ~ = 10.2 Hz, 'JHH = 2.1 Hz, 4 J= 0.8 ~ Hz), ~ 3.10 (br 8. 2H). l3C Experimental Section NMR (benzene-&, DEP"): 6 131.2 (6), 128.6 (CH), 117.3 (C), 110,7 (CHz), 109.9, 103.8, 99.5 (-CH). IR (NaC1): Y 3360 (br), Reactions with organometallic compounds were carried out 2959 (s),2925 (s),1717 (m), 1675 (s), 1629 (ss), 1569 (m), 1481 in an inert atmosphere (argon) using Schlenk type glassware (s), 1261 (ss), 1159 (s), 1092 (ss), 1016 (ss), 915 (m), 884 (m), or in a glovebox. Solvents were dried and distilled under argon 801 (s), 745 (s) cm-1. HRMS: Calcd 135.0684. Found 135.0681. prior to use. Allylmagnesium chloride was prepared according W (CHzC12, 80 pmol): Amax = 302 nm, E,,,= = 14393. Anal. to a general literature procedure.21 The organic nitriles Calcd for CgHgNO (135.1): C, 71.09; H, 6.71; N, 10.36. employed in this study were commercially available. Found: C, 71.48; H, 6.89; N, 9.76. A sample of the magnesium General Procedure for the Preparation of the 1-Aminocontaining intermediate product was dissolved in a benzene1-aryl(orhetaryl)-1,3-butadienes.To a solution of 5 mmol ddtetrahydrofuran-ds 10:1 solvent mixture. 'H NMR specof the aryl cyanide in 50 mL of ether was added dropwise a troscopy revealed an initial [Mgl-ketimine (19b): [Mgl0.48 M ethereal solution of the allylmagnesium chloride enamine (20b) ratio of 80:20 that changed during 12 h to a reagent (5 mmol) at room temperature. The reaction mixture ca. 5050 ratio. lH NMR (benzene-ddtetrahydrofuran-dg:10: was stirred for 24 h at ambient temperature and then 1)(imine:enamine: ca. 5050): [Mgl-ketimine: 6 7.70 (m, lH), concentrated in vacuo to a volume of ca. 10 mL. Pentane (25 6.50-5.80 (m, 3H), 5.25 (m, lH), 4.99 (m, lH), 3.51 (d, 2H, mL) was added and the precipitated organometallic product collected by filtration. It was suspended in ether and hydro3 J= 7.1 ~ Hz). ~ [Mgl-enamine: 6 7.70 (m, 1H), 6.50-5.80, 5.55 (br d, lH), 5.10-4.70 (each m, overlapping with imine signals). lyzed by dropwise addition of 0.1 mL of concentrated aqueous l-Amino-l-phenyl-l,3-butadiene (224. Reaction of 0.50 ammonia solution. After 10 min of stirring the ethereal phase g (4.85 mmol) of benzonitrile in 50 mL of ether with 10.5 mL was separated and dried over magnesium sulfate. Solvent was removed in vacuo to yield the l-amino-l-aryl-1,3-butadiene of a 0.48 M ethereal allylmagnesium chloride solution yielded 0.45 g (64%) of a 70:30 mixture of (2)-22c and (E)-22cas a product. yellow oil. lH NMR (&I-benzene) (2)-22c: 6 7.50-7.00 (m, l-Amino-l-(2-pyridyl)-1,3-butadiene (22a). 2-Cyanopy5H), 6.39 (m, 1H), 5.49 (dt, 1H, 3 J= ~ 11.2~Hz, 4 J= ~ 0.8 ~ ridine (0.50 g, 4.80 mmol) dissolved in 50 mL of ether was Hz), 5.13 (ddd, lH, 3 J= ~ 17.3~ Hz, 2 J= 2.2 ~ Hz, ~ JHH = 0.8 treated with 10.0 mL of a 0.48 M ethereal allyl Grignard Hz), 4.93 (ddd, 1H, 3 J= 10.3 ~ ~ Hz, 2 J= 2.3 ~ Hz, ~ 4 J= 0.8 ~ ~ solution (4.80 mmol) and worked up as described above to give Hz), 3.25 (s, 2H). (E)-22c:6 7.50-7.00 (m, 5H), 6.53 (m, lH), 0.55 g (78%) of (Z)-22aas an oil. 'H NMR (ben2ene-d~):6 8.31 (m, 1H), 7.27 (dt, 1H, 3 J= 8.2 ~ Hz, ~ 4 J= 1.0 ~ Hz), ~ 6.94 11.2~ Hz), 5.02 (ddd, 1H, 3 J= ~ 16.6~ Hz, 5.37 (d, 1H, 3 J= ~ ~ 'Hz, 4 J ~ 2~ J= 2.3 (m, 1H),6.65-6.45 (m, 2H), 5.84 (dt, 1H, 3 J ~11.1 ~ Hz, ~ JHH = 0.8 Hz), 4.72 (ddd, l H , 3 J= ~ 10.2~ Hz, 2.2 ~Hz, 4 J =~0.8~Hz), 2.88 (s, 2H). l3C NMR = 0.8 Hz), 5.23 (ddd, 1H, 3 J= 16.6 ~ ~ Hz, 2 J =~ 2.0 ~ Hz, 4 J ~ ~ 2 J = ~ = 0.8 Hz), 5.00 (ddd, 3 J= ~ 10.2~Hz, 2 J= 2.0 ~ Hz, ~ 4 J= ~ ~(chloroform-d, DEFT) (both isomers): 6 145.3, 142.4, 139.0, 137.3 (C), 134.6, 130.9, 128.6, 128.2, 128.0, 125.5 (CH), 111.6, 0.8 Hz), 4.67 (s, 2H). I3C NMR (benZene-d6,DEFT): 6 = 154.1 108.4 (CHz), 103.6, 102.5 (CH). IR (NaC1): v = 3454 (m), 3363 (C), 148.0 (CH), 131.9 (C), 135.5, 121.9, 118.9 (CHI, 111.9 (m), 3079 (m), 3056 (m), 3025 (m), 2961 (s), 2924 (m), 1629 (CH'), 101.4 (CH). IR (NaC1): v = 3467 (m), 3355 (m), 3090 (vs), 1575 (m), 1492 (m), 1445 (s), 1373 (s), 1261 (m), 1092 (s), (w), 2925 (w), 1630 (s), 1584 (vs), 1466 (vs), 1374 (SI, 1150 (SI, 1073 (s), 1027 (s), 919 (m), 870 (m), 803 (s), 761 (s), 697 (vs) 1000 (s), 887 (m), 793 (s) cm-'. HRMS: Calcd 146.08439. cm-'. HRMS: Calcd 145.08915. Found: 145.08881. UV Found: 146.08394. UV (CH2C12,117pmoL'l): A,, = 285 nm, E = 8900. (CH&12,275 ,umol/L): A,, = 302 nm, emax = 4500. (Z)-22awas irradiated in a Pyrex vessel with 350 nm light l-Amino-l-(l-tolyl)-1,3-butadiene (22d). Treatment of ratio was 80: inside a Rayonett-reactor. The (Z)-22a/(E)-22a 4-methylbenzonitrile (0.50 g, 4.26 mmol) in 50 mL of ether 20 after 10 min, 73:27 after 20 min, 66:34 after 30 min, 56:44 with 8.90 mL of a 0.48 M ethereal allylmagnesium chloride after 40 min, and remained almost constant a t 52:48 after 55 solution as described above gave 0.42 g (62%) of a 80:20 mixture of (Z)-22dand (E)-22das a yellowish oil. 'H NMR min of irradiation (as judged by 'H NMR spectroscopy in (benzene-&) (Z)-22d 6 7.32,6.90 (each d, 4H, 3 & ~= 7.8 Hz), ~ ~ Hz), 5.10 (ddd, 1H, 3 J ~ ~ 6.44 (m, lH), 5.48 (d, lH, 3 J= 11.2 (21)Benson, R. F.; Mc Kusick, B. C. Organrc Syntheses, Robjohn, N., Ed.; Wiley: New York,1963; Coll. Vol. IV, p 746. = 16.6 Hz, 2 J= 2.2 ~ Hz, ~ JHH = 0.8 Hz), 4.93 (ddd, 1H, 3 J ~ ~
Conclusions
~~~~
~
~
~
Erker et al.
5290 J. Org. Chem., Vol. 60,No.16, 1995 = 10.2 Hz, 2 J= 2.2 ~ Hz, ~ 4 J= 0.8 ~ Hz), 3.43 (9, 2H), 2.37 (8, 3H). (E)-22d 6 6.51 (m, lH), 5.39 (d, 1H, 3 J= ~ 11.0~ Hz), 5.05 (ddd, lH, 3 J= 16.6 ~ Hz, 2 J= 2.2 ~ Hz, ~ JHH= 0.8 Hz), 4.69 (ddd, 1H, 3 J= 10.2 ~ ~ Hz, 2 J= 2.2 ~ HZ, ~ 4 J= 0.8 ~ HZ), ~
3.10 (8, 2H), 2.39 (8, 3H). 13C NMR (chloroform-d, DEPT) (major isomer): 6 = 145.3,142.4,137.8 (C), 134.7,133.8,128.6, 128.7, 128.4, 126.4, 126.1, 125.4, 125.3 (CH), 118.2 (C), 111.0, 108.0 (CH2), 103.3, 101.7 (CH), 21.0, 20.9 (CH3). IR (NaC1): Y = 3459 (w), 3375 (w), 3260 (w), 3030 (SI, 2921 (SI, 1678 (m), 1632 (vs), 1608 (ve), 1568 (s), 1511 (vs), 1453 (vs), 1369 (vs), 1261 (s), 1180 (s), 1018 (s), 811 (vs), 680 (vs) cm-'. HRMS: Calcd 159.10478. Found: 169.10442. UV (CH2C12,88 pmol): A, = 267 nm, E,,,= = 14 347. 1-Amino-1-(1-naphthyl). 1,$-butadiene (22e). Reaction of 0.50 g (3.26 mmol) of 1-cyanonaphthalene in 30 mL of ether with 6.80 mL of a 0.48 M ethereal allylmagnesium chloride solution gave 0.45 g (70%) of a 85:15 mixture of (Z)-22e and (E)-22e. lH NMR (chloroform-d): (Z)-22e: 6 8.30, 8.15, 7.87, 7.50 (each m, 7H), 5.89 (m, lH), 5.74 (d, 1H, 3 J= ~ 11.0~ Hz), 4.92 (dd, l H , 'JHH = 16.4 Hz, 2 J= ~ 2.2 Hz), ~ 4.54 (dd, 1H, 3 J= ~ 10.0~ Hz, 2 J= 2.2 ~ Hz), 3.66 (s,2H). (E)-22e: 6 6.66 11.2~ Hz, 4 J= ~ 0.7 HZ), ~ 5.13, (m, 1H), 5.28 (dt, 1H, 3 J= ~ 4.98 (each m, 2H), 3.90 (s,2H). 13CNMR (chloroformd, DEPT) (major isomer): 6 144.0, 135.1, 133.5 (C), 134.8, 128.4,128.0, 126.9, 126.3, 125.8, 125.1 (CH), 111.0 (C),107.9 (CH21, 105.0 (CH). IR (NaC1): v 3468 (m), 3368 (m), 3206 (w), 3049 (m), 2968 (m), 2924 (m), 1631 (ss), 1592 (s), 1398 (s), 1361 (s), 1240 (s), 802 (ss), 779 (5s) cm-l. HRMS: Calcd 195.10480. Found: 195.10437. W (CH2C12, 205 ymol): Am= = 280 nm, emax= 5753. 1,4-Bis(l-amino-1,3-butadien-l-yl)benzene (220. Terephthalic dinitrile (0.40 g, 3.12 mmol) in 50 mL of ether was treated with 13.0 mL of a 0.48 M ethereal solution of allylmagnesium chloride. Workup as described above gave 0.43 g (65%) of 22f (three isomers, major component ca. 80%). 'H NMR (chloroform-d), (major isomer, ca 80%): 6 7.61-7.30 11.2~Hz), 5.10 (ddd, (2H), 6.54 (m, lH), 5.47 (d, lH, 3 J= ~ lH, 'Jm = 16.7 Hz, 2Jm= 1.9 Hz, 4 J= 0.8 ~ Hz), ~ 4.94 (ddd, 0.8 Hz), 10.3 Hz, 2 J= ~ 1.9 Hz, 4 J ~ ~ 3.75 (9, lH, 3 J= ~ 2H). 13C NMR (chloroform-d, DEPT), (major isomer), one C
not detected: 6 141.8, 138.8 (C), 132.1, 130.9, 126.0, 125.5 (CH), 112.1 (CH2),102.9 (CH). IR (NaC1): v = 3420 (m), 3337 (m), 3080 (w), 2966 (w), 2911 (w), 1631 (vs), 1609 (vs), 1426 (s), 1366 (s), 1261 (m), 1097 (m), 1048 (m), 1014 (m), 986 (m), 871 (vs), 848 (vs), 814 (s), 663 (8) cm-l. HRMS: Calcd 212.13135. Found: 212.13085. UV (CH2C12,75pmol/L): A,, = 271 nm, E- = 12 502. 3-Amino-l-phenyl-l,3,6-hesatriene (22g). trans-Cinnamic nitrile (0.50g, 3.87 mmol) in 50 mL of ether was treated with 8.06 mL of a 0.48 M ethereal allylmagnesium chloride solution and worked up as described above to yield 0.48 g (72%) of a 70:30 mixture of (lE,32)-22gand (L?3,3E)-22g. 'H NMR (benzene&), (major isomer): 6 7.40-6.90 (m, 6H), 6.40 (d, lH, 3 J= ~ 8.5 Hz), 6.40 (m, lH), 5.30 (d, lH, 3 J= ~ 11.3 Hz), 5.15 (ddd, lH, 'JHH = 16.6 Hz, 2 J =~2.0~Hz, 4 J= 0.8 ~ Hz), 4.96 (ddd, lH, 'JHH = 10.3 Hz, 2 J= 2.0 ~ Hz, ~ 4 J= 0.9 ~ Hz), 3.05 (s, 0.7H (major isomer (L?3,32)-22g),2.71 (8,0.3H (minor isomer)). 1% NMR (chloroform-d, DEPT), (major isomer): 6 139.8, 136.7 (C), 130.6, 128.5, 127.4, 127.2, 126.9, 126.3 (CH), 113.1 (CHz), 109.8 (CH). IR (KBr): Y = 3436 (w), 3023 (m), 2919 (s), 1635 (vs), 1623 (vs), 1600(vs),1493 (s), 1447(s),1261 (vs), 1100 (s), 1071 (s), 801 (vs), 754 (SI, 698 (vs) cm-l. HRMS: 171.1047. Found: 171.1044. UV (CH2C12,lOSpmoVL):,A = 320 nm, emax = 10 342. Anal. Calcd for C12H13N (171.2): C, 84.16; H, 7.66; N, 8.18. Found: C, 83.71; H, 7.33; N, 8.03.
Acknowledgment. Financial support from the Fonds der Chemischen Industrie, the Deutsche Forschungsgemeinschaft, and the Alfried Krupp von Bohlen und Halbach-Stifiung is gratefully acknowledged. Supporting Information Available: Full details of the ab initio calculations (GAUSSIAN92 archive entries) and copies of 1H and 13C NMR spectra (13 pages). "his material is contained in libraries on microfiche, immediately follows this article in the microfiche version of the journal, and can be ordered from the ACS; see current masthead page for ordering information. J0950378T
